Side pocket mandrels are typically installed in a string of production tubing in a well bore. The mandrel is provided with a full opening bore which is aligned with the bore of the production tubing and with a laterally offset side pocket bore which receives a side pocket well tool. Side pocket well tools can be passed through the production tubing and are retrievably seated in the side pocket bore to perform or to monitor operations in the well bore or production tubing. A side pocket well tool is retrievable and can be seated and recovered from the offset bore by use of a kickover tool, or similar tool. Side pocket well tools heretofore typically have included flow control devices, gas-lift devices, chemical injection devices and so forth, for use in conventional production operations.
In a typical construction, the side pocket mandrel has a mandrel body section with the full opening bore and the body section is connected to forged upper and lower body sections by butt welds. To latch a tool in an offset side pocket bore, a valve latching lug or clamp is located in the mandrel body to cooperate with the side pocket well tool. Welding usually requires that the assembly be heat treated to relieve stress.
In some instances, a desire has been expressed to have an single wire electrical take out from a side pocket mandrel for data transmission to the earth's surface. This can be difficult because of welding and heat treatment which can destroy or adversely affect any electrical components. Further, even when separately installed, a bottom located electrical take out is difficult because the wire is easily damaged when the production string is moved through a well bore.
In the present invention the system for manufacturing a side pocket mandrel and its construction permits an electrical takeout at the top of the mandrel and/or the bottom of the mandrel and permits installation of an inductive coupling device in the lower end of the mandrel.
One purpose of an electrical takeout on a side pocket tool is to monitor the pressure of the fluids over a period of time as a function of real time by connection of a downhole pressure measurement tool with an electrical conductor extending to the earth's surface for data transmission. In present systems to obtain a real time pressure measurement, a pressure gauge is attached to the exterior of the string of tubing. The gauge, the tubing and an attached electrical conductor wire are located in a well bore. Should a problem arise with the tool or for any other reason which might require removal of the tool, the well must be killed and the gauge retrieved with the string of tubing. Obviously, this is expensive and time consuming.
A proposed system, such as described in the OTC paper 5920, 1989 entitled "A Downhole Electrical Wet Connection System For Delivery and Retrieval of Monitoring Instruments by Wireline" uses a side pocket mandrel and pressure gauge with a downhole "wet connector" for coupling power to a tool and for read out of data. "Wet connectors" in a high pressure, corrosive environment ultimately corrode. In making up the connection, it is often difficult to make connections because of mud or debris in the well bore. Moreover, brine in the fluid causes electrical shorting of circuits. In short, an electrical wet connector is not reliable and this is particularly true over a period of time.
In another type of system known as a "Data Latch" system, a battery powered pressure gauge is installed in a mandrel which has a bypass. A wireline tool with an inductive coil is latched in the bore of the mandrel while permitting a fluid bypass. The inductive coil on the wireline tool couples to a magnetic coil in the mandrel for obtaining a read out of real time measurements. The system does not provide downhole power to the tool and battery failure requires killing the well and retrieving the tool with the well string.
Inductive coupling devices are difficult to construct for a downhole environment and yet are extremely desirable devices for downhole tools as a replacement for the above systems. Moreover, a system for real time measurement and monitoring of pressure, flow velocity, and temperature on a more or less permanent basis is highly desirable.